The present invention relates to electrolytic cells with pervious diaphragms for the production of a gas, in particular cells for the electrolysis of aqueous solutions of alkali metal chloride.
A major difficulty met with in the operation of diaphragm cells lies in the need to adjust the running of the cells to variations in the electrolysing current. When operating, the cells are in fact subjected to large periodic variations in the electrolysing current, necessitated for example by variation in the cost of electric power from the supply grid or, more generally, by economic considerations which compel industry to reduce its electrical consumption during the period of the day where domestic comsumption is large.
Experience has shown that variations in the electrolysing current density often cause serious disturbances in the operation of diaphragm cells, particularly an acceleration in the swelling of asbestos diaphragms, if certain precautions are not observed.
So as to avoid premature swelling of the asbestos diaphragms of electrolytic cells, it is proposed, in Belgian Pat. No. 711 791 of Mar. 7, 1968, in the name of Imperial Chemical Industries Ltd, to maintain the percolation rate of the electrolyte through the diaphragms substantially proportional to the electrolysing current density at all times during operation of the cell. In order to do this the pressure of a gas produced in the anode compartment or in the cathode compartment of the cell is adjusted. For this purpose, the cell is provided with a valve of variable aperture, which partially restricts an off-take pipe for the gas when the cell is operating under a nominal current density. If the electrolyzing current density falls, a proportional reduction is made in the electrolyte feed and the aperture of the valve is altered so as to alter the gas pressure in the cell and thus immediately adjust the electrolyte percolation rate through the diaphragm so that it remains at all times proportional to the electrolysing current density.